The invention relates to a method of manufacturing a liquid crystal display device comprising an orientation layer, said orientation layer being formed in contact with the surface of a mold, which mold is subsequently removed.
The invention also relates to a liquid crystal display device comprising an orientation layer and switchable liquid-crystal material.
A liquid crystal display device comprises a cell with switchable liquid-crystal material between two flat substrates on which electric conductor tracks may be present which can be used to switch the liquid-crystal material between an "on" and an "off" state in accordance with a desired pattern. To this end, one or both substrates of a so-called active display device may additionally be provided with switching elements such as transistors. Orientation layers are frequently applied between a substrate having conductor tracks and the switchable liquid-crystal material to provide the molecules of the liquid-crystal material with a parallel (homogeneous), perpendicular (homeotropic) or oblique (tilted) preferred orientation. It is possible to provide an orientation layer on one or on both sides of the cell, i.e. on one or on both substrates. Polymer layers of, for example, polyethylene or polyimide are often used for this purpose, which layers are rubbed in one direction, for example, by means of a cloth. This has the disadvantage, however, that underlying electric elements such as wiring or transistors may be damaged, for example, mechanically or by a static charge. Another type of orientation layer consists of a layer of silicon oxide which is provided at an angle by vacuum evaporation, but such layers cannot readily be manufactured on a large scale.
An alternative orientation layer for a liquid crystal display device is described in an abstract relating to the published Japanese Patent Application JP 1-94318, in Patent Abstracts of Japan, Volume 13, Number 329 (P-904) on page 122 (1989). In said abstract the orientation layers are formed in contact with the surface of a mold which is subsequently removed. The surface of the mould contacting the orientation layers to be formed is provided with a saw-tooth structure which is transferred to the surface of the orientation layers. These orientation layers, which consist of polyimide, are rubbed in the desired directions after which the cell is filled with a ferroelectric liquid-crystal material and spacers in a manner which is known per se, and then sealed. A disadvantage of this known method resides in the necessity of using a mold having an accurately mechanically machined surface. This method can only be used to obtain an orientation having a small angle of inclination. Further, an unsmooth intermediate face in the display device is undesirable because of the effects it has on the optical properties.